Hello,
If your only symptoms are just being tired, then you are probably not diabetic.
If your tiredness is accompanied with exessive thirst (you just can't get enough) and visits to the loo 5 or so times through the night, and at least once an hour during the day, then it could be diabetes.
In the mean time, if you are thirsty... dont ignore it, drink plenty of water (not lemonade, esp non diet lemonade).
Have you considered anemia? This can make you very tired too.
If you are really concerned about it being diabetes and can't wait for the Dr appt, pop down to your local pharmacy and buy a blood glucose meter, it wont cost you more than a tenner. Test your blood in the morning when you wake up (a fasting test) if it's over 7 then you could be diabetic. For a non diabetic i think typically your fasting sugar level should be about 5.
Good luck.